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(#) Checks use of resource IDs in places requiring constants

!!! WARNING: Checks use of resource IDs in places requiring constants
   This is a warning.

Id
:   `NonConstantResourceId`
Summary
:   Checks use of resource IDs in places requiring constants
Severity
:   Warning
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   4.1.0 (October 2020)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/NonConstantResourceIdDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NonConstantResourceIdDetectorTest.kt)

Avoid the usage of resource IDs where constant expressions are
required.

A future version of the Android Gradle Plugin will generate R classes
with non-constant IDs in order to improve the performance of incremental
compilation.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/SwitchTest.java:13:Warning: Resource IDs will be non-final
by default in Android Gradle Plugin version 8.0, avoid using them in
switch case statements [NonConstantResourceId]
    case R.styleable.FontFamilyFont_android_fontWeight: someValue = 1; break;
         ---------------------------------------------
src/test/pkg/SwitchTest.java:17:Warning: Resource IDs will be non-final
by default in Android Gradle Plugin version 8.0, avoid using them in
switch case statements [NonConstantResourceId]
    case R.id.text: someValue = 3; break;
         ---------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/pkg/SwitchTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

public class SwitchTest {

    SwitchTest() {}

    public int switchWithRClassReferences(int value) {
        int someValue;
        int styleableReference = R.styleable.FontFamily_fontProviderAuthority;
        switch (value) {
            // Warning: Case value is a resource and is not constant.
            case R.styleable.FontFamilyFont_android_fontWeight: someValue = 1; break;
            // No warning: Case value is not a resource and is constant.
            case 1: someValue = 2; break;
            // Warning: Case value is a resource and is constant.
            case R.id.text: someValue = 3; break;
            // The android.R class cannot be modified by the user.
            case android.R.attr.fontFamily: someValue = 5; break;
            default: someValue = 4; break;
        }
        return someValue;
    }

}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NonConstantResourceIdDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `NonConstantResourceIdDetector.test java detects constant resource ids in switch block`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("NonConstantResourceId")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("NonConstantResourceId")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection NonConstantResourceId
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="NonConstantResourceId" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'NonConstantResourceId'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore NonConstantResourceId ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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